Flat display devices, such as a liquid crystal display device, are rapidly gaining widespread use as compact and thin display devices. Among such flat display devices, a liquid crystal display device (LCD), for example, is composed of liquid crystal sealed between first and second substrates each having an electrode formed on the side opposite to each other. In a LCD displaying color images, a color filter of R, G, or B is formed corresponding to each pixel, thereby controlling the color displayed by each pixel.
FIG. 1 illustrates a circuit structure of an active matrix type LCD in which the display at each pixel is controlled by a switching element, such as a thin film transistor (TFT) connected to a pixel electrode, provided for each pixel. In such an active type LCD, the TFT and the pixel electrode are formed on the first substrate, and a common electrode is formed on the second substrate provided opposite to the first substrate. While a color filter is formed in a color active matrix LCD in addition to the above-described elements, such a color filter is usually formed on the second substrate where the above-described common electrode is formed in conventional devices.
When the color filter is formed on the second substrate, alignment between the first and second substrates must be taken into consideration, and therefore a black matrix must be formed on the second substrate to compensate for misalignment. However, the black matrix is a major cause of decreasing the aperture ratio of the LCD, and therefore improvement is required in LCDs which particularly demand higher aperture ratio.
In order to eliminate the above-described black matrix and improve the aperture ratio, an LCD of the so-called on-chip color filter configuration in which a color filter is formed on a substrate for forming the switching element (the first substrate) has been proposed. In such an on-chip color filter configuration, the need for providing the black matrix to cope with misalignment in affixing the second substrate to the first substrate can be eliminated.
FIG. 2 shows a configuration of an on-chip color filter in an active matrix LCD. On a first substrate 10, a data line and a gate line (not shown in FIG. 2) are formed in a matrix as illustrated in FIG. 1, and a TFT 2 (not shown in FIG. 2) is formed near the intersection of these lines. The gate line and the TFT are first formed on the substrate, and on an insulating film formed to cover these elements the above-described data line 30 and a color filter 50 for each pixel are formed. On the color filter 50, a pixel electrode 20 of indium tin oxide (ITO) or the like is formed connected to the TFT through a contact hole. The first substrate 10 formed as described above is affixed to a second substrate 80 having a common electrode 82 at the surface with a liquid crystal layer 70 interposed between the substrates. By controlling a voltage applied to the liquid crystal layer 70 for each pixel with the common electrode 82 and the pixel electrode 20, liquid crystal is driven and color display is presented. Use of such an on-chip color filter makes achievement of a bright color display possible.
Although color blur can be diminished by using the above-described on-chip color filter, forming a color filter of R, G, or B for a corresponding pixel requires a step of etching each color filter formed on the entire substrate away from the unnecessary pixel position so that the color filter remains only at the necessary pixel position, and this step must be performed for each of the color filters of R, G, and B.
However, formed under such color filters provided on the first substrate are the TFT for supplying a display data voltage to each pixel electrode, and wirings for supplying a display data signal and a scanning signal to the TFT, as described above. Consequently, the underlying wirings and a conductive layer of the TFT are prone to erosion and oxidation when the color filters are patterned.
Especially, the data line and the gate line are often disposed at the boundary between display electrodes. Particularly, the data line is often formed of aluminum (Al) having a high electric conductivity but susceptible to erosion and oxidation as shown in FIG. 2, and is positioned at the boundary between adjoining pixels of the color filters patterned for each pixel as illustrated in FIG. 2. When a color filter material including a negative photoresist material and pigment mixed thereto is used for the on-chip color filter configuration, the color filter can be formed to a desired shape by performing light exposure and development on the color filter. However, the data line is easily degraded by being exposed to alkali developer or the like used for patterning the color filter.
On the other hand, for an LCD with a small pixel, such as an LCD for a viewfinder, accuracy of patterning of the color filter is important because the color filter must be carefully made not to extend to the adjacent pixels. However, it is difficult to obtain color filters having a sharp outline only through developing and etching techniques because a photosensitive resin or the like is used as a primary material for the color filter and because the filter is relatively thick, making it impossible to prevent the color filter from extending to adjacent pixel regions.
In order to solve the above-described problems, an object of the present invention is to form an on-chip color filter having a sharp outline without adversely affecting underlying wirings and the like.
Another object of the present invention is to provide a method of surely preventing formation of a gap between a color filter and a substrate during transfer without adversely affecting underlying wirings and the like when the on-chip color filter is formed through a transfer method.